Benefication of siderite contaminated sand

ABSTRACT

Disclosed is a method for removing iron and other impurities from sand containing kaolin clay, siderite (FeCO3) and other mineral impurities, by subjecting the sand to the sequential processing steps of washing, anionic mineral froth floating, cationic sand froth floating, and acid leaching of the froth floated sand with sulfuric acid to yield a flint glass quality sand containing less than about 0.025% by weight of iron as Fe2O3.

United States Patent Slade Oct. 21, 1975 [54] BENEFICATION OF SIDERITE 3,374,062 3/1968 Bowdish 423/113 CONTAMINATED SAND FOREIGN PATENTS OR APPLICATIONS [75] memo" Slade Walnut Creek, 652,980 5/1951 United Kingdom 423/340 Calif.

[73] Assignee: Owens-Illinois, lnc., Toledo, Ohio Primary Examiner-Edward J. Meros Assistant Examiner-Michael L. Lewis [22] Ffled June 1973 Attorney, Agent, or FirmHoward G. Bruss, Jr.; E. J. [21] Appl. No.: 368,941 Holler [52] US. Cl. 423/340; 423/138; 423/150; ABSTRACT 2 209/166 Disclosed is a method for removing iron and other im- [51] hit. Cl. C01B 33/12 purities from Sand Containing kaolin clay Siderite [58] FIeld of Search 423/340, 113, 150, 138; (Pecos) and other mineral impurities by subjecting 209/ 18 the sand to the sequential processing steps of washing, anionic mineral froth floating, cationic sand froth [56] References C'ted floating, and acid leaching of the froth floated sand UNITED STATES PATENTS with sulfuric acid to yield a flint glass quality sand 2,409,665 10/1946 C016 et a1. 209/166 ta g l s t an a ut 0.025% by weight of iron as 2,423,022 6/1947 Herkenhoff 209/166 F6203. 2,466,987 4/1949 Herkenhoff 209/166 3,282,416 11 1966 Coke 209 166 8 Clalms, 1 Drawmg Flgure f/0,/7E fb/t ffl/rlm/fizp MAI/WW4 02 KHOA/A 44/7) @EfU/W/A/f ,QF/W/cp ,qjfl/fl/f .Y/OEZ/ff M01; .JfiP/Tt ffzb/r/ 540747/0/1/ /f //1/ flwfl f9A/0 Fzor/ N 400/7/02/42 /-7fl 74f/0/t/ J70f/T[ F M/A f MLJTUAP) w l W I J fi/l/O 7C ///l [[fla z/py g 1 ,MW/ flew/fin 50/6 4 48/0 zfcyczz' US. Patent Oct. 21, 1975 zMtW z/pwe FFc aV/ W /4A/0 F4 6 CAE BENEFICATION F SIDERITE CONTAMINATED SAND This invention relates to a process for refining sand. More particularly, this invention pertains to the refinement of sand deposits containing kaolin clay and ironbearing mineral impurities such as siderite, for use in the preparation of flint glass and ceramic products. Sand deposits commonly contain iron in various forms, and the presence of iron is undesirable because of its effect in discoloring the ultimate glass or ceramic product formed therefrom. This is especially true in the case of ceramic whiteware and flint or clear glass products.

In many sand deposits, the iron is present as free or loosely bound iron oxide which is easily removed by a simple washing procedure. In other sand deposits, the iron is tightly bound to the sand as a mineral impurity such as siderite on the quartz grains. When iron is bound in the sand in this fashion, it is quite difficult to remove within the framework of existing environmental and economic considerations.

In the past, the sand deposits containing the loosely bound iron oxide have been used to fulfill the manufacturing requirements for flint glass and ceramic whiteware. As these sand deposits become depleted and less accessible, it becomes imperative to provide methods for benefication of lower grades of sand. The present invention relates to an efficient and economical method for benefication of a siderite-containing sand. The present invention is particularly applicable to the sand deposits located near lone, California, which comprises on a weight basis about 25-30% kaolin and other clays, 5-l0% siderite, and other iron bearing mineral impurities, with the balance being silica sand.

It has been known in the past to remove mineral impurities from siliceous materials by froth flotation. For instance, U.S. Pat. No. 3,425,548 shows the use of special surfactants in floating iron and clay from sand, and U.S. Pat. No. 3,480,143 shows floating heavy minerals from siliceous materials using special surfactants.

It has also been known in the past to purify ironcontaining sand with sulfuric acids. For instance, U.S. Pat. Nos. 3,374,062, 2,891,844 and 2,306,021 disclose the purification of silica sands by treatment with hot aqueous solutions of sulfuric acids containing a soluble inorganic chloride. U.S. Pat. No. 1,957,579 teaches the process of treating sand with sulfuric acid wherein the sand is heated to about 200F. and mixed with sulfuric acid to vaporize water and liberate a film of concentrated sulfuric acid on the sand particles. U.S. Pat. No. 2,182,384 discloses the process of treating sand with sulfuric acid to remove free iron and iron compounds and then washing the dissolved iron with excess water.

None of the foregoing references are concerned with the particular and difficult problem of removing iron bound to sand in the form of siderite and do not suggest the specific economic and environmental advantages of the present invention.

The drawing represents a schematic process flow diagram of the present invention which is described in detail in the following description and example.

In the benefication of sand according to the present invention, sand containing kaolin clay and iron-bearing mineral impurities including siderite is slurried in water and the slurry deslimed and separated by density differential into an overflow phase containing kaolin clay and an underflow phase containing sand and siderite. The pH of the underflow phase is adjusted with base to in the range of 8 to 10 and an anionic collector is mixed with the underflow phase to form a first froth flotation mixture. This first froth is aerated to float a portion of the siderite in the resulting froth. The froth is removed to leave a sand-containing slurry which is mixed with cationic collector to form a second froth flotation mixture. The second froth flotation mixture is aerated to float sand, and the resulting froth is separated to leave residual siderite in the slurry. The sand is recovered from the froth and leached with aqueous sulfuric acid at a temperature and for a time sufficient to reduce the iron oxide content thereof to less than about 0.025% as Fe O the sulfuric acid leach liquor is filtered from the sand for recovery and recycling.

The washing or desliming step is performed to remove most of the kaolin clay. In this step the raw sand is slurried in water to form a slurry containing about 30 to 40% by Weight of solids. After thoroughly mixing the slurry, it is passed to a centrifugal separator of the cyclone type through which the flow rate is maintained to yield an aqueous underflow phase containing about 60 to by weight of solids, and an aqueous overflow phase containing the balance of the solids.

Under these conditions, the aqueous underflow phase from the separator contains most of the sand and siderite, while the aqueous overflow phase contains most of the kaolin and other clays. The overflow phase is known as slime because of its physical appearance and texture. The kaolin and other clays can be recovered therefrom by conventional processing techniques.

The sequential anionic siderite froth flotation and cationic sand froth are critical to the present invention. The terms anionic and cationic refer to the character of the collector employed.

Froth flotation is a process whereby one or more particulate components of a slurry are selectively caused to rise to the surface of a frothing chamber while the chamber is being aerated by sparging with air. The particles are caught in the froth formed on the surface of the chamber and removed with the froth while the particles that do not rise remain in the slurry and are drawn off through the bottom of the flotation chamber. Anionic or cationic collectors are used for frothing depending on the nature of the particles to be removed in the froth.

Froth flotation equipment for practicing the present invention can be of any conventional design wherein air or other gaseous medium is sparged through a tank containing the mineral slurry and frothing agents, collectors, and other frothing aids. The selection of the particular equipment forms no part of the present invention and details on the selection thereof can be obtained from pages 1085-1091 of the Chemical Engineers Handbook, Third Edition, McGraw-l-Iill Book Company (1950), the disclosure of which is incorporated by reference.

Collectors are organic compounds which act selectively on the surfaces of certain inorganic particles, rendering them water-repellent. Collectors concentrate on the water-particle interface, rendering the particles water-repellent and thus ensuring their attachment to air bubbles.

A typical collector requirement is about 0.5 pounds of collector per ton of solids with the extremes of about 0.1 to 10 pounds per ton depending on the ore and its condition.

In the anionic siderite flotation, carboxylic acids are used as the collectors after the pH of the flotation mixtures has been adjusted to in the range of 8 to 10 with base. It has been found that the pH range provides for most efficient flotation of the siderite. Any base such as NaOH, KOH, LiOl-I, NaCO or Ca(OH can be used to adjust the pH, although particularly efficient siderite flotation is achieved when a combination of Ca(Ol-I) and NaOH are used.

The anionic carboxylic acid collector can be any of those exhibiting functionality and can be saturated or unsaturated acids of various hydrocarbon chain lengths.

The common fatty acids are lauric acid (12C saturated), palmitic acid (16C saturated) stearic acid (18C saturated), oleic acid 18C unsaturated), linoleic (18C unsaturated), and linolenic (18C unsaturated). Mixtures of various fatty acids are present in tall oil fatty acids and these are preferred in the present process for efficiency and economy.

In the cationic sand froth flotation an amine functional cationic collector is employed. These amine functional cationic collectors are classified as primary, secondary, tertiary, and quaternary, in accordance with the number of hydrocarbon groups attached to the nitrogen atom. A further classification can be made into alkyl amines, aryl amines, and alkyl aryl amines. There are also other structures in which the nitrogen is part of a cyclic ring.

Primary amines are organic bases represented by the formula RNI-I in which R is an aliphatic chain. The primary amines with 8 to 22 carbon atoms, mixtures thereof, or various derivatives, are commercially important amine collectors.

Amines that can be used in flotation are those derived from fatty acids which occur naturally as mixtures of various chain lengths. The amine collectors include tallow fatty acids which are composed of 18C unsaturated and saturated and 16C saturated amines and coco amine, derived from coconut oil fatty acids, composed of 12C amine and small amounts of 8C through 18C amines. Substituted amines such as triethanol amine are effective. Long chain fatty aminopropyl amine derived from tallow fatty acids are preferred in the present invention. Such preferred amines can be represented by the structural formula:

wherein R is a long chain alkane, usually 8C to 22C.

In the above formula when R is 18C the name of the amine is N-octadecyl propylene diamine; and when R is 16 the name is N-hexadecyl propylene diamine and so forth. These amines are rendered cationic by reaction with an acid.

The froth flotation is carried out according to the general procedures outlined above with the sand rising in the froth and the siderite and other mineral impurities are retained in the liquid slurry. The sand is filtered from the froth to a moisture content of about 5 to to minimize the introduction of extraneous material into the subsequent leaching step.

The final step in the sequential process of this invention comprises leaching the sand recovered from the foregoing sand froth flotation process with sulfuric acid for a time and at a temperature sufflcient to reduce the iron (reported as Fe O to less than about 0.025% by weight of the sand.

While there are many combinations of sulfuric acid concentration, reaction times and temperatures, and leaching proportions, it has been found that aqueous solutions of ll0% by weight of H SO mixed with the sand in the proportion of about 60-80% of total solids with preheating of the sand, the acid, or both, so that the leaching temperature is in the range of l25200F. are particularly satisfactory. Usually the temperature of the leaching is about l50l60F. for 5 minutes to 1 hour with time periods of from about 15 minutes to 30 minutes being particularly advantageous from the standpoint of economy and efficiency.

After the leaching has been accomplished, the leach liquor is removed by filtration and the solid reaction products are removed therefrom by a sedimentational thickening process wherein the crystals of siderite and other mineral sludges are removed. The clarified leach liquor is then reconstituted to the desired acid strength with make-up sulfuric acid for reuse in the leaching operation.

This recovery and recycling technique minimizes the amount of materials that must be treated for disposal while maintaining efficiency in acid consumption.

The invention will be more clearly understood from the examples that follow wherein all parts are parts by weight, all percentages are weight percentages, and all temperatures are in degrees Fahrenheit unless stated otherwise.

EXAMPLE Basis: 2,000 pounds of raw siderite-contaminated sand.

PART A DESLIMING OF KAOLIN CLAY Raw (as mined siderite-contaminated sand), having a particle size passing a 35 mesh US. Standard Sieve, has a composition comprising about 28 weight percent kaolin and other clays, 7 weight percent siderite and additional mineral impurities, and 65 weight percent silica sand.

Two thousand pounds of raw sand is thoroughly mixed with water in the proportion of 35 parts of raw sand per 65 parts of water to form a slurry. This slurry is pumped to a cyclone type centrifugal separation (such as shown on pages 1023-1026 of the Third Edition of Chemical Engineers Handbook by J. H. Perry) where the slurry is separated by density differential into an overflow phase and an underflow phase. The flow rate through the cyclone is maintained such that the aqueous underflow phase contains 65 to 68% solids.

The aqueous underflow phase contains most of the sand and siderite while the aqueous overflow phase contains most of the kaolin and other clays. By maintaining the underflow content of solids at 65 to 68%,

the particle size of such solids are in the range of -35 to +200 mesh on a standard screen.

The overflow containing the kaolin and other clays (called slime) can be further processed to recover the clays.

The aqueous underflow from the cyclone separator is pumped to a sedimentational type rake classifier (such as shown on page 925 of Perrys' Chemical Engineers Handbook) for further removing of residual clays. The sand, siderite and any other heavy mineral impurities settle to the bottom of the classifier while the clays exit in the overflow.

The underflow from the classifier which is continually raked from the bottom of the classifier has a particle size in the range of about 35 to +200 mesh, and contains about 12-15% siderite. About 1,000 pounds of sand, siderite and heavy minerals are recovered as the underflow from the rake classifier.

PART B (SIDERITE FROTH FLOTATION) The sand and siderite containing classifier underflow from Part A is mixed with 0.2 pounds of calcium carbonate per ton to provide a product suitable for the heavy mineral flotation. The flotation mixture is loaded into an aeration flotation chamber equipped with an air sparge (such as those shown in page 1089 of Perrys Chemical Engineers Handbook) where the solids content is adjusted to 65 to 70% with water. The pH of the mixture is then adjusted to about 9 with sodium hydroxide. About 0.2 pounds of NaOH per ton of solids are required.

A tall oil fatty acid anionic collector is mixed with the flotation mixture in the proportion of 0.6 to 0.8 pounds per ton of solids. The anionic collector comprises 52% oleic acid, 45% linoleic acid, 2% linoleic acid and 2% other saturated acids such as is available from Hercules Powder Company under their designation PAMAK- WD. As a frothing aid, diesel oil is also mixed to the frothing mixture in the proportion of 0.2 to 0.3 pounds per ton of solids.

The flotation mixture is aerated according to conventional procedures and the resulting froth fraction is removed. the froth fraction contains most of the siderite and other heavy minerals while the residual liquid phase contains sand. The liquid phase is removed from the flotation chamber and further deslimed in a cyclone as described in Part A to remove any residual slime not removed in Part A or during the flotation process.

The liquid phase contains about 900 pounds of sand, which sand contains about 0.5 weight Fe O (mostIy as siderite).

Similar results are obtained when oleic acid or stearic acid is used in place of the tall oil fatty acid in the above procedures.

PART C SAND FROTH FLOTATION The sand from Part B is changed to a second flotation chamber like the one described above and water is added to the sand in a proportion such that the solids content of the resulting slurry is about 65 to 70% solids.

A cationic amine collector (a long chain fatty aminopropyl amine derived from tallow fatty acids) is neutralized with HCl to a pH of 7 and then is mixed with the slurry in the proportion of 0.5 pounds of amine per ton of solids (a suitable cationic collector is available from Ashland Chemical Company under their designation Adogen-570-S).

The flotation mixture is aerated and the air sparging rate is adjusted so of the total solids are removed with the overflow froth fraction and 5% of the solids remain in the liquid slurry. The liquid slurry contains siderite and large aggregates of sand bound together with siderite.

The sand, which is recovered from the froth fraction, contains about 0.3% weight percent Fe O and is subjected to three additional sand froth flotations as described in this Part. The sand recovered from the froth fraction from the final flotation process contains about 0.15% weight Fe O This sand is suitable for use in making green, amber or other colored glass composition, or it can be further processed as below for flint glassmaking quality.

Similar results are obtained when N-octyl propylene diamine or N-hexadecyl propylene diamine are used in place of the fatty amine propyl amine in the above procedure.

PART D SAND LEACHING WITH SULFURIC ACID The sand from Part C is vacuum filtered to contain aboot 6% moisture for leaching with sulfuric acid. The filtered sand is charged to an agitated leach chamber and 5% by weight aqueous sulfuric acid, which has been preheated to 2002l0F., is charged to the leach chamber in the proportion of 30 parts of acid per 70 parts of solids. The leach mixture is mixed for a few minutes and the resulting temperature of the leach mixture is about F. The leach mixture is allowed to stand for about 30 minutes.

After this leaching period, the leach mixture is conveyed to a vacuum filter where the leach liquor is separated from the sand without dilution. the filtered sand is then washed with dilute aqueous sodium hydroxide and water to neutralize any residual acid, and then dried in a hot air drier.

About 800 pounds of dried sand having a particle size in the range of 35 to +200 mesh screen size, the sand contains less than about 0.019% Fe O and is of flint glassmaking quality.

Experimentation with this leaching step indicates that the Fe O content of the sand is a function of the leaching time. For instance, when the leaching period is reduced from 30 minutes to 15 minutes in the above procedure, the Fe O content of the resulting sand is about 0.022%. In either case, the Fe O content is well below 0.025% which is the generally accepted maximum for flint glass-making.

PART E RECYCLE OF LEACH LIQUOR The leach liquor, removed as the filtrate in Part D, is pumped to a continuous sedimentational thickening apparatus where crystals of sideride and other sludges are removed as underflow. The overflow phase is clarified sulfuric acid to which fresh sulfuric acid is added to reconstitute a 5% by weight sulfuric acid solution. The reconstituted 5% sulfuric acid is heated to 2002l0F. for reuse in Part D.

From the foregoing, it is apparent that the present invention provides an economical and commercially practical method of beneficiating low-grade siderite sand ores for use in flint glassmaking applications. The present invention also minimizes the amounts of byproduct materials that must be processed for disposal.

Having thus described the invention, what is claimed 1. In the process for producing flint quality glassmaking sand from contaminated sand containing kaolin clay and siderite, the steps of:

admixing said contaminated sand with water to form a slurry,

centrifugally separating said slurry by density differential into an overflow phase containing kaolin clay and an underflow phase containing sand and siderite,

adjusting the pH of said underflow phase with base to in the range of 8 to 10,

mixing an anionic carboxylic acid collector with said underflow phase to form first a froth flotation mixture,

aerating said first froth flotation mixture to float a portion of said siderite in the resulting froth,

removing said froth to leave a sand-containing slurry,

mixing a cationic amine collector with said sandcontaining slurry to form a second froth flotation mixture,

aerating said second froth flotation mixture to float sand in the resulting froth, and leave residual siderite in the slurry,

removing sand from said froth,

leaching said sand with aqueous sulfuric acid at a temperature and for a time sufficient to reduce the iron oxide content thereof to less than about 0.025% as F6203, and

filtering the aqueous sulfuric acid leach liquor from the sand and drying the sand.

2. The process of claim 1 wherein said contaminaed sand comprises on a weight basis 25-30% kaolin and other clays, 5-10% siderite and other iron bearing mineral impurities, with the balance being silica sand.

3. The process of claim 1 wherein said anionic carboxylic acid collector comprises tall oil fatty acid.

4. The process of claim 1 wherein said cationic amine collector is a long chain fatty aminopropyl amine derived from tallow fatty acids.

5. The process of claim 1 wherein said sulfuric acid is an aqueous solution of about 1 to 10% by weight H 6. The process of claim 5 wherein the leaching temperature is about l25to 200F.

7. The process of claim 6 wherein the leaching time is for about 5 minutes to 1 hour.

8. The process of claim 7 wherein said leaching time is about 15 minutes to 30 minutes. 

1. IN THE PROCESS FOR PRODUCING FLINT QUALITY GLASSMAKING SAND FROM CONTAMINATED SAND CONTAINING KAOLIN CLAY AND SIDERITE, THE STEPS OF: ADMIXING SAID CONTAMINATED SAND WITH WATER TO FORM A SLURRY, CENTRIFUGALLY SEPARATING SAID SLURRY BY DENSITY DIFFERENTIAL INTO AN OVERFLOW PHASE CONTAINING KAOLIN CLAY AND AN UNDERFLOW PHASE CONTAINING SAND AND SIDERITE, ADJUSTING THE PH OF SAID UNDERFLOW PHASE WITH BASE TO IN THE RANGE OF 8 TO 10, MIXING AN ANIONIC CARBOXYLIC ACID COLLECTOR WITH SAID UNDERFLOW PHASE TO FORM FRIST A FROTH FLOTATION MIXTURE, AERATING SAID FRIST FROTH FLOTATION MIXTURE TO FLOAT A PORTION OF SAID SIDERITE IN THE RESULTING FROTH, REMOVING SAID FROTH TO LEAVE A SAND-CONTAINING SLURRY, MIXING A CATIONIC AMINE COLLECTOR WITH SAID SAND-CONTAINING SLURRY TO FORM A SECOND FROTH FLOTATION MIXTURE, AERATING SAID SECOND FROTH FLOTATION MIXTURE TO FLOAT SAND IN THE RESULTING FROTH, AND LEAVE RESIDUAL SIDERITE IN THE SLURRY, REMOVING SAND FROM SAID FROTH, LEACHING SAID SAND WITH AQUEOUS SULFURIC ACID AT A TEMPERATURE AND FOR A TIME SUFFICIENT TO REDUCE THE ION OXIDE CONTENT THEREOF TO LESS THAN ABOUT 0.025% AS FE2O3, AND FILTERING THE AQUEOUS SULFURIC ACID LEACH LIQUOR FROM THE SAND AND DRYING THE SAND.
 2. The process of claim 1 wherein said contaminaed sand comprises on a weight basis 25-30% kaolin and other clays, 5-10% siderite and other iron bearing mineral impurities, with the balance being silica sand.
 3. The process of claim 1 wherein said anionic carboxylic acid collector comprises tall oil fatty acid.
 4. The process of claim 1 wherein said cationic amine collector is a long chain fatty aminopropyl amine derived from tallow fatty acids.
 5. The process of claim 1 wherein said sulfuric acid is an aqueous solution of about 1 to 10% by weight H2SO4.
 6. The process of claim 5 wherein the leaching temperature is about 125*to 200*F.
 7. The process of claim 6 wherein the leaching time is for about 5 minutes to 1 hour.
 8. The process of claim 7 wherein said leaching time is about 15 minutes to 30 minutes. 